Preparing logs for veneering begins in the sawmill. This milling process, known as "flitching", takes place on either a circular saw or a bandsaw. Traditionally, the veneer logs have been sawn at the mill to remove the log's natural taper so that the logs are left somewhat squared at the butt end, leaving substantially no taper remaining in the log from top to bottom, as opposed to from side to side, and from the small end to the butt end--substantially all of the taper from the top to the bottom having been removed from the butt end of the log. See FIGS. 1 & 2. This squaring up process results in the removal of valuable veneer wood from the butt end of the veneer log. The squared up veneer log is then sawn in half lengthwise, and two flitches are thereby produced. The two flitches may or may not be of the same thickness, but each squared up flitch will hold substantially the same longitudinal thickness from top to bottom from its small end to its butt end. See FIG. 2.
Fifty or more flitches are placed in a vat of water at a veneer mill to be heated in preparation for slicing. They are then extracted, a few at a time, and mounted one at a time on the rotary-staylog of a conventional rotary-staylog veneer slicing machine by any number of conventional dogging (attachment) systems. The typical rotary-staylog has a cast iron body that extends the length of the cutting surface of a veneer-slicing knife. The rotary-staylog body is fixed between the lathe centers of the head stock and the tail stock of the machine and rotates between them, as would a woodturning in a conventional lathe. Presently, the preferred dogging systems in use to attach a squared up flitch to a conventional rotary-staylog veneer slicing machine require that at least two parallel grooves be cut into the flat underside of the flitch (FIG. 2), each of a sufficient size to receive a plurality of pairs of hydraulically driven clamping dogs that are spaced along the entire length of and extend about 1 in. above the rotary-staylog's mounting surface. The pairs of clamping dogs engage the flitch within the grooves when the flitch is laid flush upon the rotary staylog's mounting surface and pinch the flitch between the grooves to secure the flitch to the rotary-staylog.
The presence of grooves cut into the flat underside of the flitch results in a weakening of the edges of the flitch as the flitch's size is reduced by the slicing of veneer sheets from the flitch as it rotates on the rotary-staylog. Eventually, a springing action occurs under the hydraulic force of the clamping dogs and the veneer slicing knife as a result of the thinning of the wood between the grooves and the face of the flitch from which the veneer is being removed. This produces "shim sheets" or sheets of veneer with edge thicknesses that taper away to nothing, as opposed to sheets that maintain a consistent thickness across the entire width of the sheets. The inclusion of the "shim sheets" with the otherwise saleable veneer will result in customer dissatisfaction because these sheets will result in the rejection of veneer faces that include these thinner than allowable or "shim sheets." It is presently considered to be good practice to discard these "shim sheets" as they come off the rotary-staylog, which results in less product, lower yields, poor resource use, and less profit for the veneer mill.
It is common practice for veneer mills to plane the underside of the flitch prior to or during the grooving procedure to achieve a perfectly flat and hence more stable surface to attach, or dog, the squared up flitch to conventional rotary-staylog--it being believed that a more stable cut will be the result. This, however, requires the loss of even more material from the squared up flitch and results in less of the flitch being reduced into usable veneer. The shimming problem still occurs as before, for the wood still springs as the grooves approach the face of the flitch from which the veneer is being removed. In addition, the most modern dogging systems in use (that still require grooving) leave an unsliceable flitch core of approximately 1 in. thickness at the core's thickest point.